1. Field of the Invention
The present invention relates to a reflector for illumination apparatus and, more particularly, to an improvement of a reflector comprising a multilayered optical film for allowing infrared rays to pass therethrough and reflecting only visible light.
2. Description of the Related Art
An illumination apparatus comprising a reflection film for allowing infrared rays to pass therethrough and reflecting only visible light is known. The reflection film can allow infrared rays included in light emitted from a light source such as a filament, a discharging lamp, or the like to pass therethrough and to be radiated backward, and reflects only visible light forward. Thus, no infrared rays are projected onto an object to be illuminated, and a temperature rise of the object can be prevented.
An example of the reflection film having wavelength selectivity is a multilayered optical film. The film is prepared by stacking two or more types of thin layers of materials having different refractive indeces. The thicknesses of these layers are adjusted to strongly reflect only light components of an arbitrary wavelength. More specifically, several layers to tens of layers of these types, each having a thickness of 1/4 (where is the wavelength of the light which the film will reflect), are stacked one upon another, thus forming the reflection film. Due to the light interference among these layers, those components of the light which have specific wavelengths are strongly reflected, whereas the other components of the light pass through the layers. That is, layers of two or three types are stacked, one upon another. The layers can have a thickness of 1/8 in order to reduce the variance of degree in which the light components having wavelengths falling within the infrared range are reflected by the reflection film. Such a multilayered optical film is used to reflect only light components in the wavelength range of visible light, and to allow light components of other wavelengths, e.g., infrared rays to pass therethrough. As a result, no infrared rays are radiated on an object to be illuminated, and a temperature rise of the object can be prevented.
In an illumination apparatus comprising the multilayered optical film, a reflector body on which the film is deposited must be formed of a material having a high infrared transmission property. In a conventional illumination apparatus, the reflector is formed of a glass material. However, when the reflector is formed of the glass material, the manufacture of the reflector is cumbersome, and hence, cost is increased. In addition, the total weight is increased, and the reflector is easy to damage.
In order to eliminate such drawbacks, a reflector may be formed of a synthetic resin material. For example, in Japanese Utility Model Publication No. 47-23102, a reflector is formed of a synthetic resin film. In this utility model, the reflector is prepared such that a thermosetting synthetic resin film on which an aluminum reflection film is deposited is molded into a predetermined shape.
However, when the reflector is formed of the synthetic resin material, various problems, e.g., a problem of heat resistance, occur. More specifically, synthetic resin materials have low heat resistance, and a relatively low infrared transmittance. Therefore, when the reflector is formed of the synthetic resin material, some components of infrared rays transmitted through a multilayered optical film are absorbed in the synthetic resin material of the reflector, the temperature of the synthetic resin material is increased and may exceed the critical temperature of the heat resistance. Therefore, a reflector formed of a synthetic resin material can only be applied to an illumination apparatus which comprises a low-output light source such as a fluorescent lamp, as disclosed in Japanese Utility Model Publication No. 47-23102. The reflector disclosed in this publication has a reflection film made of aluminum, and inevitably reflects not only visible light rays but also infrared rays.